AskDefine | Define cranium

Dictionary Definition

cranium n : the part of the skull that encloses the brain [syn: braincase, brainpan] [also: crania (pl)]

User Contributed Dictionary

English

Etymology

From Medieval Latin cranium "skull", from Ancient Greek κρανίον (kranion) "upper part of the head, skull".

Pronunciation

Noun

  1. The skull of a vertebrate.
  2. That part of the skull enclosing the brain, the braincase.
  3. A trivial series of boardgames

Translations

skull
braincase

Extensive Definition

otherusesof Skull The skull is a bony structure found in the head of many animals. The skull supports the structures of the face and protects the head against injury.
The skull can be subdivided into two parts: the cranium and the mandible. A skull that is missing a mandible is only a cranium; this is the source of a very commonly made error in terminology. Those animals having skulls are called craniates.
Protection of the brain is only one part of the function of a bony skull. For example, a fixed distance between the eyes is essential for stereoscopic vision, and a fixed position for the ears helps the brain to use auditory cues to judge direction and distance of sounds. In some animals, the skull also has a defensive function (e.g. horned ungulates); the frontal bone is where horns are mounted.

Human skulls

In humans, the adult skull is normally made up of 22 bones. Except for the mandible, all of the bones of the skull are joined together by sutures, rigid articulations permitting very little movement. Eight bones form the neurocranium (braincase)—including the frontal, parietals, occipital bone, sphenoid, temporals and ethmoid—a protective vault surrounding the brain. Fourteen bones form the splanchnocranium, the bones supporting the face. Encased within the temporal bones are the six ear ossicles of the middle ears, though these are not part of the skull. The hyoid bone, supporting the tongue, is usually not considered as part of the skull either, as it does not articulate with any other bones.The skull is a protector of the brain.
The skull contains the sinus cavities, which are air-filled cavities lined with respiratory epithelium, which also lines the large airways. The exact functions of the sinuses are unclear; they may contribute to decreasing the weight of the skull with a minimal decrease in strength,or they may be important in improving the resonance of the voice. In some animals, such as the elephant, the sinuses are extensive. The elephant skull needs to be very large, to form an attachment for muscles of the neck and trunk, but is also unexpectedly light; the comparatively small brain-case is surrounded by large sinuses which reduce the weight.
The meninges are the three layers, or membranes, which surround the structures of the nervous system. They are known as the dura mater, the arachnoid mater and the pia mater. Other than being classified together, they have little in common with each other.
In humans, the anatomical position for the skull is the Frankfurt plane, where the lower margins of the orbits and the upper borders of the ear canals are all in a horizontal plane. This is the position where the subject is standing and looking directly forward. For comparison, the skulls of other species, notably primates and hominids, may sometimes be studied in the Frankfurt plane. However, this does not always equate to a natural posture in life.

Possible types of skull fractures

Other skulls

Temporal Fenestra

The temporal fenestra are anatomical features of the amniote skull, characterised by bilaterally symmetrical holes (fenestrae) in the temporal bone. Depending on the lineage of a given animal, two, one, or no pairs of temporal fenestrae may be present, above or below the postorbital and squamosal bones. The upper temporal fenestrae are also known as the supratemporal fenestrae, and the lower temporal fenestrae are also known as the infratemporal fenestrae. The presence and morphology of the temporal fenestra is critical for taxonomic classification of the synapsids, of which mammals are part.
Physiological speculation associates it with a rise in metabolic rates and an increase in jaw musculature. The earlier amniotes of the Carboniferous did not have temporal fenestrae but the more advanced sauropsids and synapsids did. As time progressed, sauropsids' and synapsids' temporal fenestrae became more modified and larger to make stronger bites and more jaw muscles. Dinosaurs, which are sauropsids, have large advanced openings and their descendants, the birds, have temporal fenestrae which have been modified. Mammals, which are synapsids, possess no fenestral openings in the skull, as the trait has been modified. They do, though, still have the temporal orbit (which resembles an opening) and the temporal muscles. It is a hole in the head and is situated to the rear of the orbit behind the eye.

Classification

There are four types of amniote skull, classified by the number and location of their fenestra. These are:
  • Anapsida - no openings
  • Synapsida - one low opening (beneath the postorbital and squamosal bones)
  • Euryapsida - one high opening (above the postorbital and squamosal bones); euryapsids actually evolved from a diapsid configuration, losing their lower temporal fenestra.
  • Diapsida - two openings
Evolutionary, they are related as follows:

See also

References

  • White, T.D. 1991. Human osteology. Academic Press, Inc. San Diego, CA.
cranium in Arabic: جمجمة
cranium in Official Aramaic (700-300 BCE): ܩܪܩܦܬܐ
cranium in Bulgarian: Череп
cranium in Catalan: Crani
cranium in Czech: Lebka
cranium in Welsh: Penglog
cranium in Danish: Kranium
cranium in German: Schädel
cranium in Dhivehi: ބޮލުގެ ނާށިގަނޑު
cranium in Estonian: Kolju
cranium in Spanish: Cráneo
cranium in Esperanto: Kranio
cranium in Basque: Burezur
cranium in Persian: جمجمه
cranium in French: Crâne
cranium in Galician: Cranio
cranium in Korean: 두개골
cranium in Croatian: Lubanja
cranium in Indonesian: Tengkorak
cranium in Ossetian: Сæргæхц
cranium in Icelandic: Höfuðkúpa
cranium in Italian: Cranio
cranium in Hebrew: גולגולת
cranium in Kurdish: Kilox
cranium in Latin: Calva
cranium in Latvian: Galvaskauss
cranium in Lithuanian: Galvos griaučiai
cranium in Hungarian: Koponya
cranium in Dutch: Schedel
cranium in Japanese: 頭蓋骨
cranium in Norwegian: Skalle
cranium in Pangasinan: Lapislapis
cranium in Polish: Czaszka
cranium in Portuguese: Crânio
cranium in Romanian: Craniu
cranium in Quechua: Uma tullu
cranium in Russian: Череп
cranium in Simple English: Skull
cranium in Slovak: Lebka
cranium in Slovenian: Lobanja
cranium in Serbian: Лобања
cranium in Finnish: Pääkallo
cranium in Swedish: Kranium
cranium in Thai: กะโหลกศีรษะ
cranium in Ukrainian: Череп
cranium in Chinese: 颅骨
Privacy Policy, About Us, Terms and Conditions, Contact Us
Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2
Material from Wikipedia, Wiktionary, Dict
Valid HTML 4.01 Strict, Valid CSS Level 2.1